Apple Mail Crashing Upon Opening

I also just noticed, if I turn off WiFi on my iMac, Mail does not even open for a few seconds. Its just opens the quit message the moment I try to open Mail.

Turn WiFi on again and it open for a few seconds, looks like its trying to download messages, but then quits again.

Hi John,

Thank you for the reply.

I should start by saying I'm a computer hack. Not my strong point so bear with me!

I followed the Step1 instruction in your link (open Mail holding Shift) but it makes no difference. Mail opens, looks normal then quits. I tried holding shift and opening, opening then hitting **** immediately, etc. Not sure how I get to Steps2-3 if it wont stay open?

I'm also not sure it related to any one message, as for the few seconds it open, I can navigate around different email, folders, etc.

I also tried shutting down and opening my iMac in Safe Mode. I've never used safe mode before, everything looked the same, but it was very responsibly slow with lots of screen flickering (I assume that means safe mode?). Mail opened and quit, much the same, only slower.

Unfortunately, it looks like I'll have to skip tot he redo all my email accounts stage.

Despite being in the suburbs of Melbourne Australia, our fasted ADSL2 speed is 3Mbs, averaging <1.5Mbs, and at this moment 0.8Mbs.

So the system just wont download the OS for reinstall.

I tried hot-spot to my mobile (usually much faster but way less data), but it did not like that either.

After hitting "continue" to start the download, it just freezes until I get the message "download failed".

Next issue, is as I noted earlier, I'm not super tech savy. Not too long ago, I had to rebuild al my mail accounts due to ISP/server issue. It took ages, I had to get IT help from my ISP and my emails (mostly business) and Mail folder system were all messed-up/lost.

I cringe at having to go through that painful process yet again simply due Mail software glitched. And mind you, Mail has been faultless ever since I transitioned to Apple five years ago.

A question... if I delete all of my many email accounts... is there a process I can use to save them in their current condition, and, be able to get back to that after redoing them all? As noted ea;rier, I did drop a copy of the User/Library Mail folder as backup.

Thank you for the replies everyone. Its been fixed, so I thought best to update this thread, as the fix was not from one of the responses here.

To be honest, I was very nervous about reinstalling the OS, resetting all email accounts, etc. It all sounded very extreme. So I ended up calling Apple support here in Australia.

I got on to two very very helpful techs, Cooper and Ricky (thank you guys, can recommend highly enough), that spent a long time on the phone with me and were very patient.

Although I am not overly techy, my gut feeling was confirmed in that earlier in the day when I tried to 'drag and drop' a Gmail storage folder (not inbox folder) to an On My Mac folder, some kind of sync issue began that was causing Mail to quit. That's why it ran and downloaded just fine, but as Mail went to then try and sync to Gmail..... crash.

It did take us a while to work out and I lost a whole day of work, but once we worked out that Mail was fine on my other devices and fine on the suspect iMac (so long as the Gmail account was inactive) the fix was simple. Delete Gmail email account from Mail and then re-add it (Now also called Google).

Just to be safe, I also did the same on my MacBook Air.

Thanks again to the support here and from Apple. My faith is returned ;-)

Note... Mail on my MacBook Air (El Captain 10.11.4) is working fine.